Butterfly

Butterflies
Cairns Birdwing, the largest butterfly in Australia (Melbourne Zoo).
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Order: Lepidoptera (unranked): Rhopalocera
Subgroups
Superfamily Hedyloidea: Hedylidae Superfamily Hesperioidea: Hesperiidae Superfamily Papilionoidea: Papilionidae Pieridae Nymphalidae Lycaenidae Riodinidae

Spider lily and butterfly Papilio xuthus Linnaeus 1767

A butterfly is an insect of the order Lepidoptera. Like all Lepidoptera, butterflies are notable for their unusual life cycle with a larval caterpillar stage, an inactive pupal stage, and a spectacular metamorphosis into a familiar and colourful winged adult form. Most species are day-flying so they regularly attract attention. The diverse patterns formed by their brightly coloured wings and their erratic yet graceful flight have made butterfly watching a hobby.

Butterflies comprise the true butterflies (superfamily Papilionoidea), the skippers (superfamily Hesperioidea) and the moth-butterflies (superfamily Hedyloidea). Butterflies exhibit polymorphism, mimicry and aposematism. Some migrate over long distances. Some butterflies have evolved symbiotic and parasitic relationships with social insects such as ants. Butterflies are important economically as agents of pollination. In addition, a few species are pests, because they can damage domestic crops and trees in their larval stage.

Culturally, butterflies are a popular motif in the visual and literary arts.

1 The four-stage lifecycle 1.1 Egg 1.2 Caterpillars 1.2.1 Wing development 1.3 Pupa 1.4 Adult or imago 2 External morphology 2.1 Scales 3 Polymorphism 3.1 Mimicry 3.2 Seasonal polyphenism 4 Habits 5 Flight 5.1 Migration 6 Defense 7 Notable species 8 In culture 8.1 Art 8.2 Symbolism 8.3 Technological inspiration 9 See also 10 Cited references 11 Other references 12 Field guides to butterflies 13 External links 13.1 General interest 13.2 Regional lists 13.3 Images/Movies

The four-stage lifecycle

Mating Common Buckeye Butterflies

Unlike many insects, butterflies do not experience a nymph period, but instead go through a pupal stage which lies between the larva and the adult stage (the imago). Butterflies are termed as holometabolous insects, and go through complete metamorphosis.

• Egg
• Larva, known as a caterpillar
• Pupa (chrysalis)
• Adult butterfly (imago)

It is a popular belief that butterflies have very short life spans. However, butterflies in their adult stage can live from a week to nearly a year depending on the species. Many species have long larval life stages while others can remain dormant in their pupal or egg stages and thereby survive winters.^[1]

Butterflies may have one or more broods per year. The number of generations per year varies from temperate to tropical regions with tropical regions showing a trend towards multivoltinism.

Egg

Egg of Ariadne merione

Butterfly eggs consist of a hard-ridged outer layer of shell, called the chorion. This is lined with a thin coating of wax which prevents the egg from drying out before the larva has had time to fully develop. Each egg contains a number of tiny funnel-shaped openings at one end, called micropyles; the purpose of these holes is to allow sperm to enter and fertilize the egg. Butterfly and moth eggs vary greatly in size between species, but they are all either spherical or ovate.

Butterfly eggs are fixed to a leaf with a special glue which hardens rapidly. As it hardens it contracts, deforming the shape of the egg. This glue is easily seen surrounding the base of every egg forming a meniscus. The nature of the glue is unknown and is a suitable subject for research. The same glue is produced by a pupa to secure the setae of the cremaster. This glue is so hard that the silk pad, to which the setae are glued, cannot be separated.

Eggs are usually laid on plants. Each species of butterfly has its own hostplant range and while some species of butterfly are restricted to just one species of plant, others use a range of plant species, often including members of a common family.

The egg stage lasts a few weeks in most butterflies but eggs laid close to winter, especially in temperate regions, go through a diapause stage, and the hatching may take place only in spring. Other butterflies may lay their eggs in the spring and have them hatch in the summer. These butterflies are usually northern species (Mourning Cloak, Tortoiseshells)

Caterpillars

Caterpillars of Junonia coenia.

Butterfly larvae, or caterpillars, consume plant leaves and spend practically all of their time in search of food. Although most caterpillars are herbivorous, a few species such as Spalgis epius and Liphyra brassolis are entomophagous (insect eating).

Some larvae, especially those of the Lycaenidae, form mutual associations with ants. They communicate with the ants using vibrations that are transmitted through the substrate as well as using chemical signals.^[2][3] The ants provide some degree of protection to these larvae and they in turn gather honeydew secretions.

Caterpillars mature through a series of stages called instars. Near the end of each instar, the larva undergoes a process called apolysis, in which the cuticle, a mixture of chitin and specialized proteins, is released from the epidermis and the epidermis begins to form a new cuticle beneath. At the end of each instar, the larva moults the old cuticle, and the new cuticle rapidly hardens and pigments. Development of butterfly wing patterns begins by the last larval instar.

Butterfly caterpillars have three pairs of true legs from the thoracic segments and up to 6 pairs of prolegs arising from the abdominal segments. These prolegs have rings of tiny hooks called crochets that help them grip the substrate.

Some caterpillars have the ability to inflate parts of their head to appear snake-like. Many have false eye-spots to enhance this effect. Some caterpillars have special structures called osmeteria which are everted to produce smelly chemicals. These are used in defense.

Host plants often have toxic substances in them and caterpillars are able to sequester these substances and retain them into the adult stage. This helps making them unpalatable to birds and other predators. Such unpalatibility is advertised using bright red, orange, black or white warning colours. The toxic chemicals in plants are often evolved specifically to prevent them from being eaten by insects. Insects in turn develop countermeasures or make use of these toxins for their own survival. This "arms race" has led to the coevolution of insects and their host plants.^[4]

Wing development

Detail of a butterfly wing

Last instar wing disk, Junonia coenia

Wings or wing pads are not visible on the outside of the larva, but when larvae are dissected, tiny developing wing disks can be found on the second and third thoracic segments, in place of the spiracles that are apparent on abdominal segments. Wing disks develop in association with a trachea that runs along the base of the wing, and are surrounded by a thin peripodial membrane, which is linked to the outer epidermis of the larva by a tiny duct.

Wing disks are very small until the last larval instar, when they increase dramatically in size, are invaded by branching tracheae from the wing base that precede the formation of the wing veins, and begin to develop patterns associated with several landmarks of the wing.

Near pupation, the wings are forced outside the epidermis under pressure from the hemolymph, and although they are initially quite flexible and fragile, by the time the pupa breaks free of the larval cuticle they have adhered tightly to the outer cuticle of the pupa (in obtect pupae). Within hours, the wings form a cuticle so hard and well-joined to the body that pupae can be picked up and handled without damage to the wings.

Pupa

Chrysalis of Gulf Fritillary

When the larva is fully grown, hormones such as prothoracicotropic hormone (PTTH) are produced. At this point the larva stops feeding and begins "wandering" in the quest of a suitable pupation site, often the underside of a leaf.

The larva transforms into a pupa (or chrysalis) by anchoring itself to a substrate and moulting for the last time. The chrysalis is usually incapable of movement, although some species can rapidly move the abdominal segments or produce sounds to scare potential predators.

The pupal transformation into a butterfly through metamorphosis has held great appeal to mankind. To transform from the miniature wings visible on the outside of the pupa into large structures usable for flight, the pupal wings undergo rapid mitosis and absorb a great deal of nutrients. If one wing is surgically removed early on, the other three will grow to a larger size. In the pupa, the wing forms a structure that becomes compressed from top to bottom and pleated from proximal to distal ends as it grows, so that it can rapidly be unfolded to its full adult size. Several boundaries seen in the adult color pattern are marked by changes in the expression of particular transcription factors in the early pupa.

Adult or imago

The adult, sexually mature, stage of the insect is known as the imago. As Lepidoptera, butterflies have four wings that are covered with tiny scales (see photo). The fore and hindwings are not hooked together, permitting a more graceful flight. An adult butterfly has six legs, but in the nymphalids, the first pair is reduced. After it emerges from its pupal stage, a butterfly cannot fly until the wings are unfolded. A newly-emerged butterfly needs to spend some time inflating its wings with blood and letting them dry, during which time it is extremely vulnerable to predators. Some butterflies' wings may take up to three hours to dry while others take about one hour. Most butterflies and moths will excrete excess dye after hatching. This fluid may be white, red, orange, or in rare cases, blue.

External morphology

Main article: Glossary of Lepidopteran terms

Parts of an adult butterfly

Butterflies have two antennae, two compound eyes, and a proboscis

Adult butterflies have four wings: a forewing and hindwing on both the left and the right side of the body. The body is divided into three segments: the head, thorax, and the abdomen. They have two antennae, two compound eyes, and a proboscis.

Scales

Butterflies are characterized by their scale-covered wings. The coloration of butterfly wings is created by minute scales. These scales are pigmented with melanins that give them blacks and browns, but blues, greens, reds and iridescence are usually created not by pigments but the microstructure of the scales. This structural coloration is the result of coherent scattering of light by the photonic crystal nature of the scales.^[5][6][7] The scales cling somewhat loosely to the wing and come off easily without harming the butterfly.

Scales on the wing give the colours

Closeup of the scales of the Inachis io

A Monarch butterfly with the scales rubbed off a section of the wing.

Polymorphism

Many adult butterflies exhibit polymorphism, showing differences in appearance. These variations include geographic variants and seasonal forms. In addition many species have females in multiple forms, often with mimetic forms. Sexual dimorphism in coloration and appearance is widespread in butterflies. In addition many species show sexual dimorphism in the patterns of ultraviolet reflectivity, while otherwise appearing identical to the unaided human eye. Most of the butterflies have a sex-determination system that is represented as ZW with females being the heterogametic sex (ZW) and males homogametic (ZZ).^[8]

Genetic abnormalities such as gynandromorphy also occur from time to time. In addition many butterflies are infected by Wolbachia and infection by the bacteria can lead to the conversion of males into females^[9] or the selective killing of males in the egg stage.^[10]

Mimicry

The Heliconius butterflies from the tropics of the Western Hemisphere are the classical model for Müllerian mimicry.^[11]

Batesian and Mullerian mimicry in butterflies is common. Batesian mimics imitate other species to enjoy the protection of an attribute they do not share, aposematism in this case. The Common Mormon of India has female morphs which imitate the unpalatable red-bodied swallowtails, the Common Rose and the Crimson Rose. Mullerian mimicry occurs when aposematic species evolve to resemble each other, presumably to reduce predator sampling rates, the Heliconius butterflies from the Americas being a good example.

Wing markings called eyespots are present in some species; these may have an automimicry role for some species. In others, the function may be intraspecies communication, such as mate attraction. In several cases, however, the function of butterfly eyespots is not clear, and may be an evolutionary anomaly related to the relative elasticity of the genes that encode the spots.^[12][13]

Seasonal polyphenism

Many of the tropical butterflies have distinctive seasonal forms. This phenomenon is termed seasonal polyphenism and the seasonal forms of the butterflies are called the dry-season and wet-season forms. How the season affects the genetic expression of patterns is still a subject of research.^[14] Experimental modification by ecdysone hormone treatment has demonstrated that it is possible to control the continuum of expression of variation between the wet and dry-season forms.^[15] The dry-season forms are usually more cryptic and it has been suggested that the protection offered may be an adaptation. Some also show greater dark colours in the wet-season form which may have thermoregulatory advantages by increasing ability to absorb solar radiation.^[16]

Habits

Antennae shape in the lepidoptera from C. T. Bingham (1905)

The Australian painted lady feeding on a flowering shrub

Butterflies feed primarily on nectar from flowers. Some also derive nourishment from pollen,^[17] tree sap, rotting fruit, dung, and dissolved minerals in wet sand or dirt. Butterflies are important as pollinators for some species of plants although in general they do not carry as much pollen load as the Hymenoptera. They are however capable of moving pollen over greater distances.^[18] Within the Lepidoptera, the Hawkmoths and the Noctuidae are dominant as pollinators.^[19]

As adults, butterflies consume only liquids and these are sucked by means of their proboscis. They feed on nectar from flowers and also sip water from damp patches. This they do for water, for energy from sugars in nectar and for sodium and other minerals which are vital for their reproduction. Several species of butterflies need more sodium than provided by nectar. They are attracted to sodium in salt and they sometimes land on people, attracted by human sweat. Besides damp patches, some butterflies also visit dung, rotting fruit or carcasses to obtain minerals and nutrients. In many species, this Mud-puddling behaviour is restricted to the males and studies have suggested that the nutrients collected are provided as a nuptial gift along with the spermatophore during mating.^[20]

Butterflies sense the air for scents, wind and nectar using their antennae. The antennae come in various shapes and colours. The hesperids have a pointed angle or hook to the antennae, while most other families show knobbed antennae. The antennae are richly covered with sensillae. A butterfly's sense of taste is coordinated by chemoreceptors on the tarsi, which work only on contact, and are used to determine whether an egg-laying insect's offspring will be able to feed on a leaf before eggs are laid on it.^[21] Many butterflies use chemical signals, pheromones, and specialized scent scales (androconia) and other structures (coremata or 'Hair pencils' in the Danaidae) are developed in some species.

Vision is well developed in butterflies and most species are sensitive to the ultraviolet spectrum. Many species show sexual dimorphism in the patterns of UV reflective patches.^[22] Color vision may be widespread but has been demonstrated in only a few species.^[23][24]

Some butterflies have organs of hearing and some species are also known to make stridulatory and clicking sounds.^[25]

Many butterflies, such as the Monarch butterfly, are migratory and capable of long distance flights. They migrate during the day and use the sun to orient themselves. They also perceive polarized light and use it for orientation when the sun is hidden.^[26]

Many species of butterfly maintain territories and actively chase other species or individuals that may stray into them. Some species will bask or perch on chosen perches. The flight styles of butterflies are often characteristic and some species have courtship flight displays. Basking is an activity which is more common in the cooler hours of the morning. Many species will orient themselves to gather heat from the sun. Some species have evolved dark wingbases to help in gathering more heat and this is especially evident in alpine forms.^[27]

Flight

Geitoneura klugii taking off

See also Insect flight

Like many other members of the insect world, the lift generated by butterflies is more than what can be accounted for by steady-state, non-transitory aerodynamics. Studies using Vanessa atalanta in a windtunnel show that they use a wide variety of aerodynamic mechanisms to generate force. These include wake capture, vortices at the wing edge, rotational mechanisms and Weis-Fogh 'clap-and-fling' mechanisms. The butterflies were also able to change from one mode to another rapidly.^[28]

Migration

The Monarch butterfly migrates large distances

Main article: Lepidoptera migration

See also Insect migration

Many butterflies migrate over long distances. Particularly famous migrations are those of the Monarch butterfly from Mexico to North America, a distance of about 4,000 to 4,800 kilometres (2500-3000 miles). Other well known migratory species include the Painted Lady and several of the Danaine butterflies. Spectacular and large scale migrations associated with the Monsoons are seen in peninsular India.^[29] Migrations have been studied in more recent times using wing tags and also using stable hydrogen isotopes.^[30][31]

Butterflies have been shown to navigate using time compensated sun compasses. They can see polarized light and therefore orient even in cloudy conditions. The polarized light in the region close to the ultraviolet spectrum is suggested to be particularly important.^[32]

It is suggested that most migratory butterflies are those that belong to semi-arid areas where breeding seasons are short.^[33] The life-histories of their host plants also influence the strategies of the butterflies.^[34]

Mosquito

Mosquito
A female Culiseta longiareolata
Conservation status
Secure
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Order: Diptera Suborder: Nematocera Infraorder: Culicomorpha Superfamily: Culicoidea Family: Culicidae
Subfamilies
Anophelinae Culicinae Toxorhynchitinae
Diversity
41 genera

For other uses, see Mosquito (disambiguation).

Mosquito (from the Spanish meaning little fly^[1]) is a common insect in the family Culicidae (from the Latin culex meaning midge or gnat^[2]). Mosquitoes resemble crane flies (family Tipulidae) and chironomid flies (family Chironomidae), with which they are sometimes confused by the casual observer.

Mosquitoes go through four stages in their life cycle: egg, larva, pupa, and adult or imago. Adult females lay their eggs in water, which can be a salt-marsh, a lake, a puddle, a natural reservoir on a plant, or an artificial water container such as a plastic bucket. The first three stages are aquatic and last 5–14 days, depending on the species and the ambient temperature; eggs hatch to become larvae, then pupae. The adult mosquito emerges from the pupa as it floats at the water surface. Adult females can live up to a month – more in captivity – but most probably do not live more than 1–2 weeks in nature.

Mosquitoes have mouthparts which are adapted for piercing the skin of plants and animals. They typically feed on nectar and plant juices. In some species, the female needs to obtain nutrients from a "blood meal" before she can produce eggs.

There are about 3,500 species of mosquitoes found throughout the world. In some species of mosquito, the females feed on humans, and are therefore vectors for a number of infectious diseases affecting millions of people per year.^[3][4]

1 Larva 2 Pupa 3 Adult 4 Feeding habits of adults 4.1 Saliva 4.2 Egg development and blood digestion 5 Distribution 5.1 Means of dispersal 6 Disease 7 Control 7.1 Organic repellents 7.2 Natural predators 8 Mosquito bites and treatment 9 Cultural views 10 Evolution 11 See also 12 References 12.1 Notes 12.2 Sources 13 External links

Larva

Anopheles larva from southern Germany, about 8 mm long

Mosquito larvae have a well-developed head with mouth brushes used for feeding, a large thorax with no legs and a segmented abdomen.

Larvae breathe through spiracles located on the eighth abdominal segment, or through a siphon, and therefore must come to the surface frequently. The larvae spend most of their time feeding on algae, bacteria, and other micro-organisms in the surface microlayer. They dive below the surface only when disturbed. Larvae swim either through propulsion with the mouth brushes, or by jerky movements of the entire body, giving them the common name of "wigglers" or "wrigglers".

Larvae develop through four stages, or instars, after which they metamorphose into pupae. At the end of each instar, the larvae molt, shedding their exoskeleton, or skin, to allow for further growth.

Pupa

The pupa is comma-shaped, as in Anopheles when viewed from the side, and is commonly called a "tumbler". The head and thorax are merged into a cephalothorax with the abdomen curving around underneath. As with the larvae, pupae must come to the surface frequently to breathe, which they do through a pair of respiratory trumpets on the cephalothorax. However, pupae do not feed during this stage. After a few days, the pupa rises to the water surface, the dorsal surface of the cephalothorax splits and the adult mosquito emerges.

Adult

Adults of the yellow fever mosquito Aedes aegypti, a typical member of the subfamily Culicinae. The male on the left, females on the right. Note the bushy antennae and longer palps in the male.

The duration from egg to adult varies considerably among species and is strongly influenced by ambient temperature. Mosquitoes can develop from egg to adult in as little as five days but usually take 10–14 days in tropical conditions. The variation of the body size in adult mosquitoes depends on the density of the larval population and food supply within the breeding water. Adult flying mosquitoes frequently rest in a tunnel that they build right below the roots of the grass.

Adult mosquitoes usually mate within a few days after emerging from the pupal stage. In most species, the males form large swarms, usually around dusk, and the females fly into the swarms to mate.

Males live for about a week, feeding on nectar and other sources of sugar. Females will also feed on sugar sources for energy but usually require a blood meal for the development of eggs. After obtaining a full blood meal, the female will rest for a few days while the blood is digested and eggs are developed. This process depends on the temperature but usually takes 2–3 days in tropical conditions. Once the eggs are fully developed, the female lays them and resumes host seeking.

The cycle repeats itself until the female dies. While females can live longer than a month in captivity, most do not live longer than 1–2 weeks in nature. Their lifespan depends on temperature, humidity, and also their ability to successfully obtain a blood meal while avoiding host defenses.

Length of the adult varies but is rarely greater than 16 mm (0.6 in)^[5], and weigh up to 2.5 mg (0.04 grain). All mosquitoes have slender bodies with three sections: head, thorax and abdomen.

The head is specialized for acquiring sensory information and for feeding. The head contains the eyes and a pair of long, many-segmented antennae. The antennae are important for detecting host odors as well as odors of breeding sites where females lay eggs. In all mosquito species, the antennae of the males in comparison to the females are noticeably bushier and contain auditory receptors to detect the characteristic whine of the female. The compound eyes are distinctly separated from one another. Their larvae only possess a pit-eye ocellus. The compound eyes of adults develop in a separate region of the head.^[6] New ommatidia are added in semicircular rows at the rear of the eye; during the first phase of growth, this leads to individual ommatidia being square, but later in development they become hexagonal. The hexagonal pattern will only become visible when the carapace of the stage with square eyes is molted.^[6] The head also has an elongated, forward-projecting "stinger-like" proboscis used for feeding, and two sensory palps. The maxillary palps of the males are longer than their proboscis whereas the females’ maxillary palps are much shorter. (This is typical for representatives of subfamilies.) As with many members of the mosquito family, the female is equipped with an elongated proboscis that she uses to collect blood to feed her eggs.

The thorax is specialized for locomotion. Three pairs of legs and a pair of wings are attached to the thorax. The insect wing is an outgrowth of the exoskeleton. The Anopheles mosquito can fly for up to four hours continuously at up to 1–2 km/h^[7] travelling up to 12 km (7.5 mi) in a night.

The abdomen is specialized for food digestion and egg development. This segmented body part expands considerably when a female takes a blood meal. The blood is digested over time serving as a source of protein for the production of eggs, which gradually fill the abdomen.

[edit] Feeding habits of adults

Aedes aegypti vector of dengue fever and yellow fever

Both male and female mosquitoes are nectar feeders, but the females of many species are also capable of hematophagy (drinking blood). Females do not require blood for their own survival, but they do need supplemental substances such as protein and iron to develop eggs.

In regards to host location, carbon dioxide and organic substances produced from the host, humidity, and optical recognition play important roles. In Aedes the search for a host takes place in two phases. First, the mosquito exhibits a nonspecific searching behavior until the perception of host stimulants then it follows a targeted approach.^[8]

Most mosquito species are crepuscular (dawn or dusk) feeders. During the heat of the day most mosquitoes rest in a cool place and wait for the evenings, although they may still bite if disturbed. Some species, like Asian tiger mosquito, are known to fly and feed during daytime.

Mosquitoes are adept at infiltration and have been known to find their way into residences via deactivated air conditioning units.^[9]

Prior to and during blood feeding, they inject saliva into the bodies of their source(s) of blood. This saliva serves as an anticoagulant: without it, the female mosquito's proboscis would quickly become clogged with blood clots. Female mosquitoes hunt their blood host by detecting carbon dioxide (CO₂) and 1-octen-3-ol from a distance.

Mosquitoes of the genus Toxorhynchites never drink blood.^[10] This genus includes the largest extant mosquitoes, the larvae of which prey on the larvae of other mosquitoes. These mosquito eaters have been used in the past as mosquito control agents, with varying success.^[11]

Saliva

In order for the mosquito to obtain a blood meal it must surmount the vertebrate physiological responses. The mosquito, as with all blood-feeding arthropods, has mechanisms to effectively block the hemostasis system with their saliva, which contains a mixture of secreted proteins. Mosquito saliva negatively affects vascular constriction, blood clotting, platelet aggregation, angiogenesis and immunity and creates inflammation.^[12] Universally, hematophagous arthropod saliva contains at least one anticlotting, one anti-platelet, and one vasodilatory substance. Mosquito saliva also contains enzymes that aid in sugar feeding^[13] and antimicrobial agents to control bacterial growth in the sugar meal.^[14] The composition of mosquito saliva is relatively simple as it usually contains fewer than 20 dominant proteins.^[15] Despite the great strides in knowledge of these molecules and their role in bloodfeeding achieved recently, scientists still cannot ascribe functions to more than half of the molecules found in arthropod saliva.^[15] One promising application is the development of anti-clotting drugs based on saliva molecules, which might be useful for approaching heart-related disease, because they are more user-friendly blood clotting inhibitors and capillary dilators.^[16]

It is now well recognized that the feeding ticks, sandflies, and, more recently, mosquitoes have an ability to modulate the immune response of the animals (hosts) they feed on.^[12] The presence of this activity in vector saliva is a reflection of the inherent overlapping and interconnected nature of the host hemostatic and inflammatory/immunological responses and the intrinsic need to prevent these host defenses from disrupting successful feeding. The mechanism for mosquito saliva-induced alteration of the host immune response is unclear, but the data has become increasingly convincing that such an effect occurs. Early work described a factor in saliva that directly suppresses TNF-α release, but not antigen-induced histamine secretion, from activated mast cells.^[17] Experiments by Cross et al. (1994) demonstrated that the inclusion of Ae. aegypti mosquito saliva into naïve cultures led to a suppression of interleukin (IL)-2 and IFN-γ production, while the cytokines IL-4 and IL-5 are unaffected by mosquito saliva.^[18] Cellular proliferation in response to IL-2 is clearly reduced by prior treatment of cells with SGE.^[18] Correspondingly, activated splenocytes isolated from mice fed upon by either Ae. aegypti or Cx. pipiens mosquitoes produce markedly higher levels of IL-4 and IL-10 concurrent with suppressed IFN-γ production.^[19] Unexpectedly, this shift in cytokine expression is observed in splenocytes up to 10 days after mosquito exposure, suggesting that natural feeding of mosquitoes can have a profound, enduring, and systemic effect on the immune response.^[19]

T cell populations are decidedly susceptible to the suppressive effect of mosquito saliva, showing enhanced mortality and decreased division rates.^[20] Parallel work by Wasserman et al. (2004) demonstrated that T- and B-cell proliferation was inhibited in a dose dependent manner with concentrations as low as 1/7th of the saliva in a single mosquito.^[21] Depinay et al. (2005) observed a suppression of antibody-specific T cell responses mediated by mosquito saliva and dependent on mast cells and IL-10 expression.^[22] A recent study suggests that mosquito saliva can also decrease expression of interferon−α/β during early mosquito-borne virus infection.^[23] The contribution of type I interferons (IFN) in recovery from infection with viruses has been demonstrated in vivo by the therapeutic and prophylactic effects of administration of IFN-inducers or IFN,^[24] and recent research suggests that mosquito saliva exacerbates West Nile virus infection,^[25] as well as other mosquito-transmitted viruses.^[26]

Egg development and blood digestion

Two important events in the life of female mosquitoes are egg development and blood digestion. After taking a blood meal the midgut of the female synthesizes proteolytic enzymes that hydrolyze the blood proteins into free amino acids. These are used as building blocks for the synthesis of egg yolk proteins.

In the mosquito Anopheles stephensi Liston, trypsin activity is restricted entirely to the posterior midgut lumen. No trypsin activity occurs before the blood meal, but activity increases continuously up to 30 hours after feeding, and subsequently returns to baseline levels by 60 hours. Aminopeptidase is active in the anterior and posterior midgut regions before and after feeding. In the whole midgut, activity rises from a baseline of approximately 3 enzyme units (EU) per midgut to a maximum of 12 EU at 30 hours after the blood meal, subsequently falling to baseline levels by 60 hours. A similar cycle of activity occurs in the posterior midgut and posterior midgut lumen, whereas aminopeptidase in the posterior midgut epithelium decreases in activity during digestion. Aminopeptidase in the anterior midgut is maintained at a constant low level, showing no significant variation with time after feeding. alpha-glucosidase is active in anterior and posterior midguts before and at all times after feeding. In whole midgut homogenates, alpha-glucosidase activity increases slowly up to 18 hours after the blood meal, then rises rapidly to a maximum at 30 hours after the blood meal, whereas the subsequent decline in activity is less predictable. All posterior midgut activity is restricted to the posterior midgut lumen. Depending upon the time after feeding, greater than 25% of the total midgut activity of alpha-glucosidase is located in the anterior midgut. After blood meal ingestion, proteases are active only in the posterior midgut. Trypsin is the major primary hydrolytic protease and is secreted into the posterior midgut lumen without activation in the posterior midgut epithelium. Aminopeptidase activity is also luminal in the posterior midgut, but cellular aminopeptidases are required for peptide processing in both anterior and posterior midguts. Alpha-glucosidase activity is elevated in the posterior midgut after feeding in response to the blood meal, whereas activity in the anterior midgut is consistent with a nectar-processing role for this midgut region.^[27]

Distribution

A mosquito inside a home in Victoria, Australia

While many species are native to tropical and subtropical regions, some such as Aedes have successfully adapted themselves to cooler regions. In the warm and humid tropical regions, they are active the entire year long; however, in temperate regions they hibernate over winter. Eggs from strains in the temperate zones are more tolerant to the cold than ones from warmer regions.^[28][29] They can even tolerate snow and temperatures under freezing. In addition, adults can survive throughout winter in suitable microhabitats.^[30]

Means of dispersal

Over large distances the worldwide distribution is carried out primarily through sea routes, in which the eggs, larvae, and pupae in combination with water-filled used tires and cut flowers are transported around. As with sea transport, the transport of mosquitoes in personal vehicles, delivery trucks, and trains plays an important role.

Disease

Anopheles albimanus mosquito feeding on a human arm. This mosquito is a vector of malaria and mosquito control is a very effective way of reducing the incidence of malaria.

Main article: mosquito-borne disease

Mosquitoes are a vector agent that carries disease-causing viruses and parasites from person to person without catching the disease themselves.

The principal mosquito borne diseases are the viral diseases yellow fever and dengue fever, transmitted mostly by the Aedes aegypti, and malaria carried by the genus Anopheles. Though originally a public health concern, HIV is now thought to be almost impossible for mosquitoes to transmit^[31].

Mosquitoes are estimated to transmit disease to more than 700 million people annually in Africa, South America, Central America, Mexico and much of Asia with millions of resulting deaths. At least 2 million people annually die of these diseases.

Methods used to prevent the spread of disease, or to protect individuals in areas where disease is endemic include Vector control aimed at mosquito eradication, disease prevention, using prophylactic drugs and developing vaccines and prevention of mosquito bites, with insecticides, nets and repellents. Since most such diseases are carried by "elderly" females, scientists have suggested focusing on these to avoid the evolution of resistance^[32]

Control

Larvae in stagnant water

Main article: Mosquito control

There are many methods used for mosquito control. Depending on the situation, source reduction, biocontrol, larviciding (control of larvae), or adulticiding (control of adults) may be used to manage mosquito populations.

These techniques are accomplished using habitat modification, such as removing stagnant water and other breeding areas, pesticide like DDT, natural predators, (eg Dragonflies, larvae-eating fish), and trapping.

Organic repellents

With increasing reports of the harmful effects DEET, the chemical found in artifically produced mosquito repellent, has on humans, there has been a gradual move to rely on repellents that are devoid of DEET, specifically to repellents that are organic and otherwise are of the kind that have had traditional household purposes prior to their becoming used now more often as mosquito repellents.^[33] In fact, according to a study conducted by a chemist team headed by Sen-Sung Cheng of the National Taiwan University, such organic remedies include using cinnamon oil as an effective killer of mosquito hatchlings, which may also act as an effective repellent on fully grown mosquitoes that feed off of humans; other effective oils that have shown to be increasingly used as repellents include citronella oil, lemmon eucalyptus oil, rosemary oil, cedar oil, peppermint oil and clove oil.^[34] Garlic oil concentrate will repel mosquitos for up to 4 weeks.

Natural predators

Dragonflies are natural predators of mosquitoes.

The dragonfly eats mosquitoes at all stages of development and is quite effective in controlling populations.^[35] Although bats and Purple Martins can be prodigious consumers of insects, many of which are pests, less than 1% of their diet typically consists of mosquitoes. Neither bats nor Purple Martins are known to control or even significantly reduce mosquito populations.^[36] Some cyclopoid copepods are predators on 1st instar larvae, killing up to 40 Aedes larvae per day.^[37] Larval Toxorhynchites mosquitoes are known as natural predators of other Culicidae. Each larva can eat an average of 10 to 20 mosquito larvae per day. During its entire development, a Toxorhynchites larva can consume an equivalent of 5,000 larvae of the first instar (L1) or 300 fourth instar larvae (L4) (Steffan & Evenhuis, 1981; Focks, 1982). However, Toxorhynchites can consume all types of prey, organic debris (Steffan & Evenhuis, 1981), or even exhibit cannibalistic behavior. A number of fish are also known to consume mosquito larvae, including bass, bluegill, piranha, catfish, fathead minnows, the western mosquitofish (Gambusia affinis), goldfish, guppies, and killifish.

Also, Bacillus thuringiensis israelensis has been used to control them as a biological agent.

[edit] Mosquito bites and treatment

Mosquito prefer some people over others. The preferential victim's sweat simply smells better than others because of the proportions of the carbon dioxide, octenol and other compounds that make up body odour ^[38].

Visible, irritating bites are due to an immune response from the binding of IgG and IgE antibodies to antigens in the mosquito's saliva. Some of the sensitizing antigens are common to all mosquito species, whereas others are specific to certain species. There are both immediate hypersensitivity reactions (Types I & III) and delayed hypersensitivity reactions (Type IV) to mosquito bites (see Clements, 2000).

There are several commercially available anti-itch medications, including those taken orally, such as Benadryl, or topically applied antihistamines and, for more severe cases, corticosteroids such as hydrocortisone and triamcinolone. Many ineffective home remedies exist, including calamine lotion. A paste of meat tenderizer containing papain and water breaks down the proteins in the mosquito saliva. Both using a brush to scratch the area surrounding the bite and running hot water (around 49 °C) over it can alleviate itching for several hours by reducing histamine-induced skin blood flow.^[39] On the other hand, excessive scratching can irritate the bite and break the skin, leading to prolonged recovery and the possibility of infection or scarring.^{[citation needed]}

[edit] Cultural views

A mosquito in Baltic amber

According to the “Mosquitoes” chapter in Kwaidan: Stories and Studies of Strange Things, by Lafcadio Hearn (1850–1904), mosquitoes are seen in Japanese popular belief as reincarnations of the dead, condemned by the errors of their former lives to the condition of Jiki-ketsu-gaki, or "blood-drinking pretas".^[40]

Evolution

The Culicinae and Anopheles clades are believed to have diverged about 150 million years ago.^[41] The Old and New World Anopheles species are believed to have subsequently diverged about 95 million years ago.^[41]

See also

• Insect repellent
• Cymbopogon
• Anti-itch drug
• Octenol

[edit] References

[edit] Notes

1. ^ Mosquito at dictionary.com.
2. ^ Culex at dictionary.com.
3. ^ Molavi, Afshin (2003-06-12). "Africa's Malaria Death Toll Still "Outrageously High"". National Geographic. http://news.nationalgeographic.com/news/2003/06/0612_030612_malaria.html. Retrieved 2007-07-27.
4. ^ "Mosquito-Borne Diseases" – The American Mosquito Control Association. Retrieved 2008-10-14.
5. ^ "Mosquito". http://www.ext.vt.edu/departments/entomology/factsheets/mosquito.html. Retrieved 2007-05-19.
6. ^ ^{a b} Harzsch, S.; Hafner, G. (2006), "Evolution of eye development in arthropods: Phylogenetic aspects", Arthropod Structure and Development 35 (4): 319–340, doi:10.1016/j.asd.2006.08.009, http://linkinghub.elsevier.com/retrieve/pii/S1467803906000570
7. ^ Kaufmann C, Briegel H (June 2004). "Flight performance of the malaria vectors Anopheles gambiae and Anopheles atroparvus" (PDF). J. Vector Ecol. 29 (1): 140–53. PMID 15266751. http://www.sove.org/Journal%20PDF/June%202004/Kaufmann.pdf. Retrieved 2009-06-21.
8. ^ R.G. Estrada-Franco & G.B. Craig (1995) Biology, disease relationship and control of Aedes albopictus. Pan American Health Organization, Washington DC: Technical Paper No. 42.
9. ^ Rest boxes as mosquito surveillance tools
10. ^ The carnivores, Toxorhynchites
11. ^ http://www.pestscience.com/PDF/BNIra56.PDF
12. ^ ^{a b} Ribeiro JM, Francischetti IM (2003). "Role of arthropod saliva in blood feeding: sialome and post-sialome perspectives". Annu. Rev. Entomol. 48: 73–88. doi:10.1146/annurev.ento.48.060402.102812. PMID 12194906.
13. ^ Grossman GL, James AA (1993). "The salivary glands of the vector mosquito, Aedes aegypti, express a novel member of the amylase gene family". Insect Mol. Biol. 1 (4): 223–32. doi:10.1111/j.1365-2583.1993.tb00095.x. PMID 7505701.
14. ^ Rossignol PA, Lueders AM (1986). "Bacteriolytic factor in the salivary glands of Aedes aegypti". Comp. Biochem. Physiol., B 83 (4): 819–22. doi:10.1016/0305-0491(86)90153-7. PMID 3519067.
15. ^ ^{a b} Valenzuela JG, Pham VM, Garfield MK, Francischetti IM, Ribeiro JM (2002). "Toward a description of the sialome of the adult female mosquito Aedes aegypti". Insect Biochem. Mol. Biol. 32 (9): 1101–22. doi:10.1016/S0965-1748(02)00047-4. PMID 12213246.
16. ^ Dr. Nigel Beebe, University of Technology, Sidney, Australia
17. ^ Bissonnette EY, Rossignol PA, Befus AD (1993). "Extracts of mosquito salivary gland inhibit tumour necrosis factor alpha release from mast cells". Parasite Immunol. 15 (1): 27–33. doi:10.1111/j.1365-3024.1993.tb00569.x. PMID 7679483.
18. ^ ^{a b} Cross ML, Cupp EW, Enriquez FJ (1994). "Differential modulation of murine cellular immune responses by salivary gland extract of Aedes aegypti". Am. J. Trop. Med. Hyg. 51 (5): 690–6. PMID 7985763.
19. ^ ^{a b} Zeidner NS, Higgs S, Happ CM, Beaty BJ, Miller BR (1999). "Mosquito feeding modulates Th1 and Th2 cytokines in flavivirus susceptible mice: an effect mimicked by injection of sialokinins, but not demonstrated in flavivirus resistant mice". Parasite Immunol. 21 (1): 35–44. doi:10.1046/j.1365-3024.1999.00199.x. PMID 10081770.
20. ^ Wanasen N, Nussenzveig RH, Champagne DE, Soong L, Higgs S (2004). "Differential modulation of murine host immune response by salivary gland extracts from the mosquitoes Aedes aegypti and Culex quinquefasciatus". Med. Vet. Entomol. 18 (2): 191–9. doi:10.1111/j.1365-2915.2004.00498.x. PMID 15189245.
21. ^ Wasserman HA, Singh S, Champagne DE (2004). "Saliva of the Yellow Fever mosquito, Aedes aegypti, modulates murine lymphocyte function". Parasite Immunol. 26 (6-7): 295–306. doi:10.1111/j.0141-9838.2004.00712.x. PMID 15541033.
22. ^ Depinay N, Hacini F, Beghdadi W, Peronet R, Mécheri S (2006). "Mast cell-dependent down-regulation of antigen-specific immune responses by mosquito bites". J. Immunol. 176 (7): 4141–6. PMID 16547250.
23. ^ Schneider BS, Soong L, Zeidner NS, Higgs S (2004). "Aedes aegypti salivary gland extracts modulate anti-viral and TH1/TH2 cytokine responses to sindbis virus infection". Viral Immunol. 17 (4): 565–73. doi:10.1089/vim.2004.17.565. PMID 15671753.
24. ^ Taylor JL, Schoenherr C, Grossberg SE (1980). "Protection against Japanese encephalitis virus in mice and hamsters by treatment with carboxymethylacridanone, a potent interferon inducer". J. Infect. Dis. 142 (3): 394–9. PMID 6255036.
25. ^ Schneider BS, Soong L, Girard YA, Campbell G, Mason P, Higgs S (2006). "Potentiation of West Nile encephalitis by mosquito feeding". Viral Immunol. 19 (1): 74–82. doi:10.1089/vim.2006.19.74. PMID 16553552.
26. ^ Schneider BS, Higgs S (May 2008). "The enhancement of arbovirus transmission and disease by mosquito saliva is associated with modulation of the host immune response". Trans. R. Soc. Trop. Med. Hyg. 102 (5): 400–8. doi:10.1016/j.trstmh.2008.01.024. PMID 18342898. http://linkinghub.elsevier.com/retrieve/pii/S0035-9203(08)00053-9.
27. ^ Billingsley PF, Hecker H (1991). "Blood digestion in the mosquito, Anopheles stephensi Liston (Diptera: Culicidae): activity and distribution of trypsin, aminopeptidase, and alpha-glucosidase in the midgut". J Med Entomol. 28 (6): 865–71. PMID 1770523.
28. ^ Hawley WA, Pumpuni CB, Brady RH, Craig GB (March 1989). "Overwintering survival of Aedes albopictus (Diptera: Culicidae) eggs in Indiana". J. Med. Entomol. 26 (2): 122–9. PMID 2709388.
29. ^ Hanson SM, Craig GB (September 1995). "Aedes albopictus (Diptera: Culicidae) eggs: field survivorship during northern Indiana winters". J. Med. Entomol. 32 (5): 599–604. PMID 7473614.
30. ^ Romi R, Severini F, Toma L (March 2006). "Cold acclimation and overwintering of female Aedes albopictus in Roma". J. Am. Mosq. Control Assoc. 22 (1): 149–51. doi:10.2987/8756-971X(2006)22[149:CAAOOF]2.0.CO;2. PMID 16646341.
31. ^ Can I get HIV from mosquitoes? CDC 20-October-2006
32. ^ Resistance is Useless The Economist 8-April-2009
33. ^ DEET Health Effects in Humans -- DEET Chemical Technical Summary for Public Health and Public Safety Professionals, Agency for Toxic Substances and Disease Registry, December 6, 2004: http://www.atsdr.cdc.gov/consultations/deet/health-effects.html
34. ^ "How to Get Rid of Mosquitoes and Help Prevent a Stinging Encounter With Them". citing Journal of Agricultural and Food Chemistry 52: 4395-4400. 2004. http://yourhandymanzone.com/Your_Handyman_Zone_How_To_Pages_Home_Improvement_Zone_Bug_Insect_Pest_Control_Mosquitoes.htm.
35. ^ Singh RK, Dhiman RC, Singh SP (June 2003). "Laboratory studies on the predatory potential of dragon-fly nymphs on mosquito larvae". J Commun Dis 35 (2): 96–101. PMID 15562955.
36. ^ Fradin MS (01 June 1998). "Mosquitoes and mosquito repellents: a clinician's guide". Ann. Intern. Med. 128 (11): 931–40. PMID 9634433. http://www.annals.org/cgi/pmidlookup?view=long&pmid=9634433.
37. ^ Marten GG, Reid JW (2007). "Cyclopoid copepods". J. Am. Mosq. Control Assoc. 23 (2 Suppl): 65–92. doi:10.2987/8756-971X(2007)23[65:CC]2.0.CO;2. PMID 17853599.
38. ^ "Olfaction: Mosquito receptor for human-sweat odorant", Nature 427: 212–213, 2004, doi:doi:10.1038/427212a, http://www.nature.com/nature/journal/v427/n6971/full/427212a.html?lang=en
39. ^ Yosipovitch, Gil; Katherine Fast, Jeffrey D. Bernhard. "Noxious Heat and Scratching Decrease Histamine-Induced Itch and Skin Blood Flow". Journal of Investigative Dermatology 2005 (125): 1268–1272. doi:10.1111/j.0022-202X.2005.23942.x. http://www.nature.com/jid/journal/v125/n6/pdf/5603667a.pdf. Retrieved 2009-05-30.
40. ^ Hearn, Lafcadio. Kwaidan: Stories and Studies of Strange Things. Dover Publications, Inc., 1968 (ISBN 0-486-21901-1)
41. ^ ^{a b} Calvo E, Pham VM, Marinotti O, Andersen JF, Ribeiro JM (2009). "The salivary gland transcriptome of the neotropical malaria vector Anopheles darlingi is thought to reveal accelerated evolution of genes relevant to hematophagy" (PDF). BMC Genomics 10 (1): 57. doi:10.1186/1471-2164-10-57. http://www.biomedcentral.com/content/pdf/1471-2164-10-57.pdf. Retrieved 2009-06-21.

[edit] Sources

• Clements, Alan (1992). The biology of mosquitoes. 1: Development, Nutrition and Reproduction. London: Chapman & Hall. ISBN 0-85199-374-5.
• Davidson, Elizabeth W. (1981). Pathogenesis of invertebrate microbial diseases. Montclair, N.J: Allanheld, Osmun. ISBN 0-86598-014-4.
• Jahn GC, Hall DW, Zam SG (1986). "A comparison of the life cycles of two Amblyospora (Microspora: Amblyosporidae) in the mosquitoes Culex salinarius and Culex tarsalis". Coquillett. J. Florida Anti-Mosquito Assoc. 57: 24–7.
• Kale, H.W., II. (1968). "The relationship of purple martins to mosquito control". The Auk 85: 654–61.

• Brunhes, J.; Rhaim, A.; Geoffroy, B. Angel G. Hervy P. Les Moustiques de l'Afrique mediterranéenne French/English. Interactive identification guide to mosquitoes of North Africa, with database of information on morphology, ecology, epidemiology, and control. Mac/PC Numerous illustrations. IRD/IPT [12640] 2000 CD-ROM. ISBN 2-7099-1446-8 Mosquito species can also be identified through their DNA, however this is relatively expensive so it is not commonly performed. See the Use of DNA in forensic entomology.